The Carpetbagger cites Republicans opposing the amendment because it would prevent an extension of the tax deferrals which are going to impoverish the my generation's government. Someone is going to pay for the enormous debt Republicans have run up, and that means someone will have to make tough choices, probably a tax hike of some sort. Hence, tax deferrals.

If Roberts or Brownback took fiscal responsibility seriously, they would have supported this amendment, then found a way to cut spending to pay for actual tax cuts (cuts in taxation which are matched by cuts in overall spending).